As a slight diversion but in keeping with this, I flew the ILS into Oxford yesterday using vertical path mode on the autopilot. Pretty impressive watching it fly the step down fixes during the procedural approach.
You can see the track if you zoom in the oxford at the end of this log and select indicated altitude.
Pretty impressive watching it fly the step down fixes during the procedural approach.
It should not fly more than a straight line FAF-MAP, no following of SDFs.
Why do you say that Peter? It flies the published step downs - look at the plot. Then from FAF it obviously flies the glideslope.
OK; I see it now. Could not see the graph at first.
Yes, after the FAF it should be just a single straight line, even if the plate shows stepdowns. Or maybe that's a wrong way to put it, because LNAV+V is probably available only on plates which have been re-drafted to remove any post-FAF stepdowns.
I think Jasons is flying the ILS which is à continuous decent approach but was referring to the part before? the intercept part and the VNV feature in the G1000 or whatever hè is flying?
Peter wrote:
It should not fly more than a straight line FAF-MAP, no following of SDFs.
If the aircraft has G1000 system with VNV, then it will fly any step downs except the one between the IF or fix prior to the FAF. VNV uses a Baro-VNAV computer that is not certified for approach. The VNV function can fly descents based on adding the desired altitude to the flightplan waypoint. The default values in the flightplan are the minimums for the segment, so it flies the segments with a glidepath indication for each descent and autopilot mode that flies it. The GS has three indications, a green diamond for an ILS, a purple diamond for RNAV vertical guidance, and purple > for VNV Baro VNAV descents. Although the VNV can't be used for the segment that ends at the FAF, it is usually OK, because the aircraft is below the GS and will intercept and capture the GS at the higher altitude. I guess proper technique would be to manually command a descent to the proper GS intercept altitude, but in my experience it is a waste of effort. For the final approach segment, the ILS GS, RNAV GS or RNAV advisory GS is used.
The advisory GS is generally close to a straight line descent between the FAF altitude and THRE over the threshold. If there is a step down inside the FAF, the straight line is moved if needed so that it clears the step down fix which increases the angle and means that one would be past the FAF before picking up the advisory glidepath. If the math doesn't work out exactly, this is because the GS angle is based on a Baro VNAV path which follows the curvature of the earth. Usually this will be within 20 feet of the indicated straight line altitude at the FAF where a SBAS generated GS is a straight line in space, but appears to an observer on the earth as curving upward the further from the runway.
Yes it was a procedural ILS.
VNAV works well also for the 'descend when ready to FL240 be level 10 miles before XYZ'.
Achim,
Next time you are close by, try one of those:
At EDDF
RNAV 07C Y GPS LNAV+V
RNAV 07R Y GPS LNAV+V
RNAV 25C Y GPS LNAV+V
RNAV 25L Y GPS LNAV+V
At EDLN
VOR 13 or RNAV 13 GPS LNAV+V
VOR 31 or RNAV 31 GPS LNAV+V
At EDQM
NDB/DME 09 or RNAV GPS 09 LNAV+V
NDB/DME 27 or RNAV GPS 27 LNAV+V
Hi Antek,
thanks. Does that mean the LNAV+V show up as separate entries under the PROC menu on the 430, in addition to the standard RNAV entries? Where did you get that list? I will check with the 430 tomorrow, unfortunately that unit is not designed to be taken home and so far I don't have a hangar in my house yet (and no permission to taxi on my street and take off on the highway either).
Maybe I should try EDDF as you suggested, I can already imagine the laughter on the radio when I ask ATC for a practise approach to test LNAV+V 
All these procedures should be in the current cycle of the Jeppesen's Worldwide Aviation Database on your GNSS430.'
In EDLN and EDQM, RNAV GPS procedures are basically "overlays" of the old VOR and NDB/DME approaches, but they all have +V guidance (in your GNSS430, "LNAV+V" would appear in the bottom right-hand corner of the approach preview window after you had selected both the
"underlying" procedure and one of the transitions). All procedures I listed for EDDF are uniquely RNAV GPS LNAV+V let-downs.
Have fun :)
